Telescopic supports are used in a wide range of applications, including applications related to table and desk supports. In these applications, the telescopic support is often times disposed between a base and a tabletop to enable vertical adjustment of the tabletop. This conventional adjustable height table can be found in a variety of configurations and settings, such as in overbed tables for use in hospitals.
Conventional telescopic supports, in some cases, utilize an inner tube, an outer tube, and bearings therebetween. In this conventional configuration, the bearings are disposed to try to maintain axial alignment of the inner and outer tubes while allowing vertical movement of the tubes with respect to each other. The bearings also are disposed in a fixed relationship to one of the inner or outer tubes, and ride on a race disposed on or forming a part of the other of the inner or outer tubes. The race is aligned with the central or longitudinal axis of the support tubes. The primary purpose of this conventional configuration is to allow the telescopic support to extend and retract. However, as the telescopic support extends, the conventional bearing configuration often times loses its ability to maintain axial alignment under bending, torsional, or axial loads, or a combination thereof. If axial alignment is not maintained, the telescopic support may seem to tip or wobble, either of which can be unpleasant in the context of a tabletop.
An example construction of a conventional telescopic support is depicted in FIG. 1. As can be seen, the telescopic support includes a generally four sided inner tube and a generally four sided outer tube. Both tubes are formed of extruded aluminum. There are only two sets of bearings: one set of bearings is fixed to one side of the outer tube, and another set of bearings is fixed to the other side of the outer tube. Each of the two bearing sets includes four roller bearings, two bearings disposed with their rotational axis directed substantially away from the longitudinal axis of the conventional support, and the other two roller bearings disposed with their rotational axis directed substantially toward the longitudinal axis of the conventional support. Due to tolerance variations inherent to the aluminum extrusion process, the distance between the bearings and associated race surfaces can vary from one part to another. These variations can affect the ability to consistently manufacture a telescopic support that maintains axial alignment under various loads, and can result in significant wobble.
Conventionally, in an attempt to maintain axial alignment and counter the tolerance variations inherent to the aluminum extrusion process, one or more mounting or spacer blocks for each bearing set have been individually sized and machined to achieve a target clearance between the inner tube and the bearings. Incorporating such a machined spacer into the support, with dimensions specific to the support, provides a way to control the clearance between (a) the inner tube and (b) the two roller bearings of each set that have their rotational axis directed substantially away from the longitudinal axis of the support. Because these bearings are on opposite sides of the inner tube, reducing the clearance with the machined spacer can yield a fair degree of stability in axial alignment despite different loading conditions. However, it should not go unnoticed that this manufacturing process involves producing a machined part specific to the dimensions of each piece of extruded aluminum in the support. This process of measuring, machining and fitting a non-standard spacer for each support can be laborious and expensive. In other words, machining and fitting a non-standard spacer specific to the dimensions of each support can add significant cost to the support. Additionally, attempts to repair such a support can be impeded because non-standard parts can be laborious and costly to replace.